Internal handling of hash keys has changed. The old hashtable
API is still fully supported, and will likely remain so. The additions to the
API allow passing keys as
SV*s, so that tied hashes can be given real scalars as keys rather than plain strings (nontied
hashes still can only use strings as keys). New extensions must use the new
hash access functions and macros if they wish to use SV* keys. These additions also make it feasible to manipulate HE*s (hash entries), which can be more efficient. See the perlguts manpage for details.